How to create an index for elements of an array in PostgreSQL?

Question

With this schema:

create table object (
   obj_id      serial      primary key,
   name        varchar(80) not null unique,
   description text,
   tag_arr            


        

Answer 1

You can create GIN indexes on any 1-dimensional array with standard Postgres.
Details in the manual here (last chapter).

While operating with integer arrays (plain int4, not int2 or int8 and no NULL values) the additional supplied module intarray provides a lot more operators and typically superior performance. Install it (once per database) with:

CREATE EXTENSION intarray;

You can create GIN or GIST indexes on integer arrays. There are examples in the manual.
CREATE EXTENSION requires PostgreSQL 9.1 or later. For older versions you need to run the supplied script.